An energy equation, describing the spontaneous heating of coal, was integrated numerically using a digital computer. The development and operation of a program to accomplish this formed the main part of the work. The program finally developed enabled variations to be made in such external parameters as size of heap, air velocity, ambient humidity, and initial moisture content of the coal. This was done in order to investigate the mechanism of spontaneous combustion in New Zealand sub-bituminous coal, particularly the influence of moisture transfer. The computer simulation of the behaviour of coal under various conditions of storage yielded temperature profiles for coal heaps. It also illustrated the movement of water through a heap under the influence of temperature gradients and showed the importance of this effect on the development of spontaneous heating.